1. Field of the Invention
The present invention relates to a loudspeaker for high frequencies.
2. Background Art
It is known that a loudspeaker includes a sound-generating vibrating diaphragm, said diaphragm being connected for this purpose to a moving electromagnetic coil suspended in the air gap created by the pole pieces of a permanent magnet and supplied with an electric current representative of the sounds to be reproduced.
Although not exclusively, the present invention relates more particularly to a compression-chamber loudspeaker. It is known that, contrary to direct-radiation loudspeakers, compression-chamber loudspeakers do not radiate into the air medium directly, but via an acoustic horn. Such loudspeakers therefore include an acoustic horn, generally removable, and a compression-chamber motor.
In regard to said compression-chamber motor, there are essentially two different embodiments which are known and marketed.
In a first already very old embodiment, the diaphragm of the loudspeaker is made in the form of a rigid spherical cap, often metallic and fixed onto the chassis of said loudspeaker by means of a peripheral flexible suspension. The moving electromagnetic coil is connected to the periphery of said diaphragm, between said diaphragm and said suspension, and, during motion, it displaces said cap as a whole in the manner of an infinitely rigid piston. It will be noted that, by virtue of its flexibility, said suspension has the function of displacing and guiding the moving part of the loudspeaker.
This embodiment has a number of drawbacks, in particular:
the moving coil must displace the entire mass of the moving part of the loudspeaker, thus limiting the emission of sounds at high frequencies and presupposes in particular the use of heavy and expensive magnets to compensate for this defect; PA1 for reasons of loudspeaker performance, the materials used must be as light as possible while remaining extremely rigid. Beryllium is for example used to make said diaphragm, this of course increasing the cost of these loudspeakers; and PA1 it is necessary to provide a phasing piece of extremely complex design and construction, since it is necessary to make the elementary radiation from each part of the surface of the diaphragm converge in phase at the mouth of the horn. PA1 to emit sounds at high frequencies; PA1 to use a simple and inexpensive phasing piece; and PA1 to develop the sound-generating pressure variation, opposite the electromagnetic coil, this being favorable to the production of high frequencies. PA1 it can emit sounds at high frequencies, at least up to 16 kHz for certain embodiments; PA1 it can be constructed, like the associated phasing piece, simply and at low cost, since its structure is of the annular type; PA1 it exhibits a sizable emissive area for a specified diameter of the coil; and PA1 the diaphragm can be made from a material, for example a composite material or a polymer with high Young's modulus, which is less expensive than that used in the aforesaid known embodiments, since it is no longer required to be almost infinitely rigid. PA1 firstly, if it were attempted to adjoin an annular part external to the moving coil to said "CSD" type diaphragm, with a view to rendering the diaphragm annular, the sound flux developed by this external annular part would not be able to converge on the mouth of the horn in the same time as the sound flux developed by the internal annular part, dooming in this case this enhancement; PA1 secondly, the horn or waveguide is opposite the concave side of said diaphragm and not the convex side, as in the present invention; PA1 thirdly, the pressure inlet of the mouth of the horn is not situated directly opposite the moving coil, as in the case of the invention.
In a second embodiment, corresponding to a compression-chamber tweeter loudspeaker, the diaphragm comprises a rigid central annular part and a likewise rigid peripheral annular part, connected together along an annular junction situated opposite the horn of said loudspeaker. Said annular parts are moreover connected to the chassis of said loudspeaker via elastic suspensions, said elastic suspensions being formed by flexibilizing lines concentric with said annular parts, and generally made in the latter. In this embodiment, the diaphragm also moves in the manner of an extremely rigid piston.
The loudspeaker thus constructed makes it possible in particular:
However, this embodiment has the major drawback that the diaphragm, with too small an area, and whose suspension is too rigid, does not allow this loudspeaker to operate above 500 Hz.